Implementation and Characterization of Three-Dimensional Particle-in-Cell Codes on MIMD
A three-dimensional electrostatic particle-in-cell (PIC) plasma simulation code has been developed.
Massively Parallel Supercomputers↗
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Ion thruster life models
In this paper we review the most recent 2-D and 3-D plasma simulation models for ion thruster hollow cathodes, discharge chambers, and ion optics.
grid life↗
Space Flight Plasma Data Analysis
This slide presentation reviews a method to analyze the plasma data that is reported on board the International Space station (ISS). The Floating Potential Measurement Unit (FPMU), the role of which is to obtain floating potential and ionosphere plasma measurements for validation of the ISS charging model, assess photo voltaic array variability and interpreting IRI predictions, is composed of four probes: Floating Potential Probe (FPP), Wide-sweep Langmuir Probe (WLP), Narrow-sweep Langmuir Probe (NLP) and the Plasma Impedance Probe (PIP). This gives redundant measurements of each parameter. There are also many 'boxes' that the data must pass through before being captured by the ground station, which leads to telemetry noise. Methods of analysis for the various signals from the different sets are reviewed. There is also a brief discussion of LP analysis of Low Earth Orbit plasma simulation source.
Wright, Kenneth H.↗
Splanchnic Compression Improves the Efficacy of Compression Stockings to Prevent Orthostatic Intolerance
Purpose: Post-spaceflight orthostatic intolerance (OI) is observed in 20-30% of astronauts. Previous data from our laboratory suggests that this is largely a result of decreased venous return. Currently, NASA astronauts wear an anti-gravity suit (AGS) which consists of inflatable air bladders over the calves, thighs and abdomen, typically pressurized from 26 to 78 mmHg. We recently determined that, thigh-high graded compression stockings (JOBST , 55 mmHg at ankle, 6 mmHg at top of thigh) were effective, though to a lesser degree than the AGS. The purpose of this study was to evaluate the addition of splanchnic compression to prevent orthostatic intolerance. Methods: Ten healthy volunteers (6M, 4F) participated in three 80 head-up tilts on separate days while (1) normovolemic (2) hypovolemic w/ breast-high compression stockings (BS)(JOBST(R), 55 mmHg at the ankle, 6 mmHg at top of thigh, 12 mmHg over abdomen) (3) hypovolemic w/o stockings. Hypovolemia was induced by IV infusion of furosemide (0.5 mg/kg) and 48 hrs of a low salt diet to simulate plasma volume loss following space flight. Hypovolemic testing occurred 24 and 48 hrs after furosemide. One-way repeated measures ANOVA, with Bonferroni corrections, was used to test for differences in blood pressure and heart rate responses to head-up tilt, stand times were compared using a Kaplan-Meyer survival analysis. Results: BS were effective in preventing OI and presyncope in hypovolemic test subjects ( p = 0.015). BS prevented the decrease in systolic blood pressure seen during tilt in normovolemia (p < 0.001) and hypovolemia w/o countermeasure (p = 0.005). BS also prevented the decrease in diastolic blood pressure seen during tilt in normovolemia (p = 0.006) and hypovolemia w/o countermeasure (p = 0.041). Hypovolemia w/o countermeasure showed a higher tilt-induced heart rate increase (p = 0.022) than seen in normovolemia; heart rate while wearing BS was not different than normovolemia (p = 0.353). Conclusion: BS may be an effective countermeasure to post-space flight OI. The addition of splanchnic compression is more effective than the previous thigh-high garments. These stockings are readily available, inexpensive, and can be worn for days following landing as astronauts re-adapt to Earth gravity.
Platts, Steven H.↗
Space Weather Models and Their Validation and Verification at the CCMC
The Community Coordinated l\lodeling Center (CCMC) is a US multi-agency activity with a dual mission. With equal emphasis, CCMC strives to provide science support to the international space research community through the execution of advanced space plasma simulations, and it endeavors to support the space weather needs of the CS and partners. Space weather support involves a broad spectrum, from designing robust forecasting systems and transitioning them to forecasters, to providing space weather updates and forecasts to NASA's robotic mission operators. All of these activities have to rely on validation and verification of models and their products, so users and forecasters have the means to assign confidence levels to the space weather information. In this presentation, we provide an overview of space weather models resident at CCMC, as well as of validation and verification activities undertaken at CCMC or through the use of CCMC services.
Hesse, Michael↗
Comparison of Computed and Measured Performance of a Pulsed Inductive Thruster Operating on Argon Propellant
Pulsed inductive plasma accelerators are electrodeless space propulsion devices where a capacitor is charged to an initial voltage and then discharged through a coil as a high-current pulse that inductively couples energy into the propellant. The field produced by this pulse ionizes the propellant, producing a plasma near the face of the coil. Once a plasma is formed if can be accelerated and expelled at a high exhaust velocity by the Lorentz force arising from the interaction of an induced plasma current and the magnetic field. A recent review of the developmental history of planar-geometry pulsed inductive thrusters, where the coil take the shape of a flat spiral, can be found in Ref. [1]. Two concepts that have employed this geometry are the Pulsed Inductive Thruster (PIT)[2, 3] and the Faraday Accelerator with Radio-frequency Assisted Discharge (FARAD)[4]. There exists a 1-D pulsed inductive acceleration model that employs a set of circuit equations coupled to a one-dimensional momentum equation. The model was originally developed and used by Lovberg and Dailey[2, 3] and has since been nondimensionalized and used by Polzin et al.[5, 6] to define a set of scaling parameters and gain general insight into their effect on thruster performance. The circuit presented in Fig. 1 provides a description of the electrical coupling between the current flowing in the thruster I1 and the plasma current I2. Recently, the model was upgraded to include an equation governing the deposition of energy into various modes present in a pulsed inductive thruster system (acceleration, magnetic flux generation, resistive heating, etc.)[7]. An MHD description of the plasma energy density evolution was tailored to the thruster geometry by assuming only one-dimensional motion and averaging the plasma properties over the spatial dimensions of the current sheet to obtain an equation for the time-evolution of the total energy. The equation set governing the dynamics of the coupled electrodynamic-current sheet system is composed of first-order, coupled ordinary differential equations that can be easily solved numerically without having to resort to much more complex 2-D finite element plasma simulations.
Polzin, Kurt A.↗
Long-Duration Wear Testing of the ASTRAEUS Thruster, Phase I: 50 kg Xe Throughput
The thruster component of the Ascendant Sub-kW Transcelestial Electric Propulsion System successfully completed a propellant throughput demonstration of 50 kg Xe. The thruster was operated for a total of 3,287 h, of which 97.9% was spent at 300 V – 1000 W, and generated 790 kN-s of total impulse. Thrust, telemetry, and temperature measurements periodically recorded at four operating conditions spanning 200 – 500 V and 200 – 1000 W revealed constant performance across the full test duration. High-fidelity plasma simulations of the erosion of the thruster’s downstream faces suggest a theoretical lifetime capability of >30 kh, corresponding to propellant throughput of >450 kg Xe and a total impulse of >7 MNs, at the 300 V – 1000 W operating condition. The test was voluntarily paused after 50 kg Xe throughput to take these erosion measurements before the test was resumed at a different operating condition.
Goebel, Dan↗
Long-Duration Wear Testing of the ASTRAEUS Hall Thruster, Phases II & III: 72 kg Xe Throughput & 1.2 MN-s Total Impulse
The thruster component of the Ascendant Sub-kW Transcelestial Electric Propulsion System successfully completed a propellant throughput demonstration of 72 kg Xe in a long-duration wear test planned to eventually exceed 100 kg. The thruster has been operated for a total of 5450 h over three operating conditions: 3287 h at 300 V – 1000 W, 1745 h at 500 V – 1000 W, and 417 h at 400 V – 600 W. A total of 1.2 MN-s of impulse has been demonstrated to date. Thrust, telemetry, and temperature measurements periodically recorded at four operating conditions spanning 200 – 500 V and 200 – 1000 W revealed constant performance across the full test duration. The erosion of the downstream faces of the thruster was observed to be higher than anticipated after the first 5032 h of thruster operation. This issue was traced to the application of sub-nominal magnetic field strengths throughout the LDWT, caused by an electrical-related ground-support equipment issue, which resulted in a downstream shift of the discharge plasma and enhanced erosion of the thruster’s pole covers. Nevertheless, the thruster performance and operational behaviour remained unaffected. High-fidelity plasma simulations of the erosion of the thruster’s downstream faces, supported by prior short-duration wear testing, suggest a theoretical lifetime capability of >30 kh, corresponding to propellant throughput of >450 kg Xe and a total impulse of >7 MNs, at the 300 V – 1000 W operating condition. The test was voluntarily paused after 68 kg Xe and 72 kg Xe throughput, respectively, to take these erosion measurements at the 500 V and 400 V operating conditions before the test was resumed at a different operating condition.
Goebel, Dan↗
Plasma processing of SRF cavities at Jefferson Lab: Experiment results and simulation insight
Plasma processing of superconducting radio frequency (SRF) cavities has been an active research effort at Jefferson Lab (JLab) since 2019, aimed at enhancing cavity performance by removing hydrocarbon contaminants and reducing field emission. In this experiment, processing using argon-oxygen and helium-oxygen gas mixtures to find minimum ignition power at different cavity pressure was investigated. Ongoing simulations are contributing to a better understanding of the plasma surface interactions and the fundamental physics behind the process. These simulations, combined with experimental studies, guide the optimization of key parameters such as gas type, RF power, and pressure to ignite plasma using selected higher-order mode (HOM) frequencies. This paper presents experimental data from argon-oxygen and helium-oxygen gas mixture C75 and C100 cavity plasma ignition studies, as well as simulation results for the C100-type cavity based on the COMSOL model previously applied to the C75 cavity.
Accelerator Physics↗
Dust on a surface in a plasma: A charge simulation
An electrically isolated particle on a substrate surface will be electrically charged when a plasma is applied above it. We show that the magnitude of this charge is determined by a balance of the impeding ion and electron fluxes that are strongly influenced by the nearby substrate. By simulating this process, we find that the charge density of the particle can be much higher than that of the substrate. This is due to the height of the particle, which causes additional electron collection.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
High-Fidelity Simulations of Plasma-Assisted Oxidation of Hydrocarbon Fuels Using Nanosecond Pulsed Discharges
Next, a robust and efficient framework for simulating NSPD in multiple dimensions is developed. The reactive Navier-Stokes equations are extended to include a drift-diffusion plasma-fluid model with a local field approximation (LFA) in a finite-volume solver, which uses an adaptive mesh refinement (AMR) strategy to address the wide separation of length scales in the problem. A two-way coupling strategy is used whereby the plasma-fluid model and reactive Navier-Stokes equations are integrated simultaneously. The oxidation of ethylene/air mixtures mediated by NSPD is simulated in a pin-to-pin configuration. All phases of the plasma discharge are simulated explicitly (including streamer ignition, propagation, and connection, as well as the subsequent spark phase), along with the evolution of the plasma during the inter-pulse period. Temporally and spatially-resolved results are presented, with an emphasis on the analysis of heating and energy deposition, as well as of the evolution of the concentration of active particles generated during the NSPD and their influence on ignition.
adaptive mesh refinement↗
Numerical simulations of magnetospheric plasmas - Review and quadrennial report to the IUGG
This article provides a broad survey of U.S. progress during the quadrennium 1983-1986 in the category 'numerical simulations of magnetospheric plasmas'. There has been a substantial increase of activity in this area during this period. Simulations have been instrumental in providing valuable insights into large scale dynamic phenomena, nonlinear effects, and complex kinetic phenomena in a wide variety of subject areas, including shocks and double layers, ionosphere-magnetosphere coupling phenomena, and important microphysical processes such as broadband electrostatic noise. The methodology of computer simulation has also been advanced during this quadrennium. Vlasov algorithms have been improved; hybrid codes in 2 and 3D have been developed and applied to magnetospheric problems; and complex problems have been subjected with increasing frequency to a multipronged attack in which several types of simulation models, each designed to accurately model phenomena within a particular range of temporal or spatial scales, are employed synergistically.
Palmadesso, Peter J.↗
Mesh refinement for anisotropic diffusion in magnetized plasmas
Highly accurate simulation of plasma transport is needed to drive the successful design and operation of magnetically confined fusion reactors. Unfortunately, the extreme anisotropy present in magnetized plasmas results in thin boundary layers that are expensive to resolve. Here, this work investigates how various mesh refinement strategies might reduce that expense to allow for more efficient simulation by comparing standard variable refinement approaches that use a field quantity to an adaptive approach that uses an error estimator. It is first verified that higher order discretization only realizes the proper rate of convergence once the mesh resolves the thin boundary layer, therefore motivating the focusing of refinement on the boundary layer. For three two-dimensional test cases that contain characteristic features of tokamak magnetic fields, an exponential refinement strategy based on the magnetic flux function, which is the standard refinement approach in the field, is compared to an adaptive strategy utilizing the established Zienwiekicz and Zhu error estimator. The adaptive mesh refinement strategy consistently achieves the same accuracy using orders of magnitude less degrees of freedom than either exponential or uniform refinement. This result makes the adaptive refinement strategy more efficient than the exponential refinement strategy while also being more generalizable to problems with complex magnetic geometries. Scaling laws are derived that quantify the improvement in cost of the adaptive refinement strategy over other refinement approaches in 2D and 3D.
97 MATHEMATICS AND COMPUTING↗
Full-torus impurity transport simulation for optimizing plasma discharge operation using a multi-species impurity powder dropper in the large helical device
The transport of impurities supplied by a multi-species impurity powder dropper (IPD) in the large helical device (LHD) is investigated using a three-dimensional peripheral plasma fluid code (EMC3-EIRENE) coupled with a dust transport simulation code (DUSTT). The trajectories of impurity powder particles (Boron, Carbon, Iron, and Tungsten) dropped from the IPD and the impurity transport in the peripheral plasma are studied in a full-torus geometry. The simulation reveals an appropriate size of the impurity powder particles and an optimum operational range of the dust drop rates for investigating the impurity transport without inducing radiation collapse. The simulation also predicts a favourable plasma discharge condition for wall conditioning (boronization) using the IPD in order to deposit boron to high plasma flux and neutral particle density areas in the divertor region in the inboard side of the torus.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Simulation Study of the Influence of Experimental Variations on the Structure and Quality of Plasma Liners
Simulation studies of a section of a spherically imploding plasma liner, formed by the merger of six hypersonic plasma jets, have been performed at conditions relevant to the Plasma Liner Experiment (PLX) [S. C. Hsu et al., IEEE Trans. Plasma Sci. 46, 1951 (2018)]. The main aim of simulations was the sensitivity study of the detailed structure of plasma liners and their global properties to experimental mass variations and timing jitter across the six plasma jets. Experimentally observable synthetic quantities have been computed using simulation data and compared with the available experimental data. Simulations predicted that the primary oblique shock wave structure is preserved at small experimental variations. At later phases of the liner implosion, primary shocks and, especially, secondary shocks are more sensitive to experimental variations. These conclusions follow from the simulation data as well as the experimental CCD camera images. Small displacements of the shock wave structures may also cause significant changes in the synthetic interferometer data at early time. Our studies showed that the global properties of the plasma liners (averaged Mach number and averaged ram pressure along leading edges of plasma liners) are not very sensitive to experimental variations. Simulation data of the liner structure were largely confirmed by the PLX experimental data.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A conservative scheme for electromagnetic simulation of magnetized plasmas with kinetic electrons
A conservative scheme has been formulated and confirmed for gyrokinetic particle simulations of electromagnetic waves and instabilities in magnetized plasmas. An electron continuity equation derived from the drift kinetic equation is used to time advance the electron density perturbation by using the perturbed mechanical flow calculated from the parallel vector potential, and the parallel vector potential is solved by using the perturbed canonical flow from the perturbed distribution function. In gyrokinetic particle simulations using this new scheme, the shear Alfvén wave dispersion relation in the shearless slab and continuum damping in the sheared cylinder have been recovered. The new scheme overcomes the stringent requirement in the conventional perturbative simulation method that perpendicular grid size needs to be as small as electron collisionless skin depth even for the long wavelength Alfvén waves. The new scheme also circumvents the problem in the typical approach that an unphysically large parallel electric field arises due to the inconsistency between electrostatic potential calculated from the perturbed density and vector potential calculated from the perturbed canonical flow. Lastly, the gyrokinetic particle simulations of the Alfvén waves in sheared cylinder have superior numerical properties compared with the fluid simulations, which suffer from numerical difficulties associated with singular mode structures.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Modern gyrokinetic particle-in-cell simulation of fusion plasmas on top supercomputers
The Gyrokinetic Toroidal Code at Princeton (GTC-P) is a highly scalable and portable particle-in-cell (PIC) code. It solves the 5D Vlasov-Poisson equation featuring efficient utilization of modern parallel computer architectures at the petascale and beyond. Motivated by the goal of developing a modern code capable of dealing with the physics challenge of increasing problem size with sufficient resolution, new thread-level optimizations have been introduced as well as a key additional domain decomposition. GTC-P's multiple levels of parallelism, including inter-node 2D domain decomposition and particle decomposition, as well as intra-node shared memory partition and vectorization have enabled pushing the scalability of the PIC method to extreme computational scales. In this paper, we describe the methods developed to build a highly parallelized PIC code across a broad range of supercomputer designs. This particularly includes implementations on heterogeneous systems using NVIDIA GPU accelerators and Intel Xeon Phi (MIC) co-processors and performance comparisons with state-of-the-art homogeneous HPC systems such as Blue Gene/Q. New discovery science capabilities in the magnetic fusion energy application domain are enabled, including investigations of Ion-Temperature-Gradient (ITG) driven turbulence simulations with unprecedented spatial resolution and long temporal duration. Performance studies with realistic fusion experimental parameters are carried out on multiple supercomputing systems spanning a wide range of cache capacities, cache-sharing configurations, memory bandwidth, interconnects and network topologies. Furthermore, these performance comparisons using a realistic discovery-science-capable domain application code provide valuable insights on optimization techniques across one of the broadest sets of current high-end computing platforms worldwide.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Numerical simulations of auroral plasma processes. I - Ion beams and conics. II - Electric fields
The characteristics of ion beams and conics as seen in two-dimensional numerical simulations in which the plasmas are driven by current sheets of a finite thickness are described. It is shown that the most energetic ions in the simulations have pitch angles near 90 deg, implying a large perpendicular acceleration of the ions. Large perpendicular electric fields, similar to those measured in electrostatic shocks, are mainly confined near the edges of the current sheets, where E-perpendicular is much larger than E-parallel. Double layers with E-perpendicular about equal to, and spatially separated from, E-parallel form in the interior of wide current sheets. Such double layers have upward electric fields in the region of the upward current. Downward electric fields develop outside the current sheet.
Singh, Nagendra↗